The advent behind microbial fuel cells (MFC) is to provide clean electricity from the waste organic material. The MFC produces electricity with the help of microorganisms. In the present review, the biocatalysts or microorganisms used in the MECs are discussed. The most used microorganisms in the MFCs belong to Shewanella, Proteobactor and Pseudomonas families. In waste water based MFCs. mixed cultures are mostly used. This review covers the biocatalysts used in both anode and cathode. In the recent times, one of the most valuable development in the MFCs is the use of biocathodes, which eliminated various drawbacks of these cells and enhanced the power generation capabilities as well as the production of some useful gases like hydrogen. The present state of art of this technology still requires development in certain power output areas such as improvement of efficiency and cost reduction. (c) 2010 Elsevier Inc. All rights reserved.